The invention concerns a lubricant composition that can be washed off cold and a dry lubricant composition as well as their use for application on a metal strip as corrosion protection, washing and/or forming lubricant.
Lubricants have various tasks in metal working. In the rolling mill, rolling oils or rolling emulsions are used which are applied on the metal strip in order to affect the friction conditions between roller and strip for an optimal rolling result. Rolling oils differ—depending on metal and tool—in the viscosity and in the presence and the concentration of additives for improving the lubricating action, polar and non-polar additives. Typical additives are extreme-pressure (EP) additives and anti-wear additives such as sulfur or phosphorus carriers as well as corrosion inhibitors, for example, sulfonates.
After rolling, in the steel mill (or aluminum plant) a corrosion protection agent is usually applied on the surface of the metal strips for preventing corrosion during storage and transport. In this way, the autoadhesion of metal strips that are stacked or wound to a coil (strip coil) is prevented also. Prior to working, for example, in a pressing or a stamping tool or in another metal working tool, this corrosion protection agent is removed by means of a washing oil or an alkaline cleaner and, for example, a drawing or stamping oil is applied that reduces the friction during forming of the metal strip and thereby facilitates working and ensures improved forming results or reduces the number of faulty formed products.
As corrosion protection agent for steel and aluminum strips or coils, mostly water-immiscible oils or wax-like products, so-called hot melts, are used which are also water-immiscible.
The washing, drawing, stamping or other forming oils used in the metal working plant can be, for example, aqueous emulsions or aqueous synthetic solutions or medium- to high-viscosity oil formulations.
It is important in all employed lubricants that they have a satisfactory compatibility with the entire process. Particularly in the automotive field, there are high requirements for keeping expenditure and number of steps following metal working as low as possible, with minimal rejects at the same time, for example, visible faults in the final coat due to lubricant residues. The surfaces of the produced pressed parts manufactured from the steel or aluminum strips are cleaned—optionally after assembly of pressed parts with conventional joining methods—prior to performing the subsequent treatment steps such as phosphatization, passivation, and electrophoretic dip coating. For cleaning, usually aqueous alkaline cleaners are employed which, in case of automotive bodies in white, preferably are comprised of a two-component system comprised of: a salt structure (builder) component and a surfactant component. The cleaning action is realized mostly by a spraying/dipping method at typical application temperatures of 50 to 60° C.
As an alternative to a pure corrosion protection agent, a so-called pre-lube can be applied in the steel mill or aluminum plant after rolling for final working of the rolled goods.
Pre-lubes are compositions that combine the properties of a corrosion protection oil with the lubricating action of a drawing oil. Like the corrosion protection agents, the pre-lubes prevent corrosion and adhesion during transport and storage of the metal strip coils but serve at the same time as drawing lubricant in the pressing plant. In case of pre-lubes, it is also very important, particularly in the automotive field, that an excellent compatibility exists with every individual process from cold strip to the body in white. When the pre-lube is compatible with every process step (in particular, welding, gluing etc.) including painting in the production chain, a significant reduction of the number and quantity of the lubricants employed in the pressing plant (washing oils, drawing, stamping or other forming oils) as well as of the working steps to be performed is enabled.
DE 2 207 504 A discloses an emulsifiable lubricant or slip agent for cold forming of metals that can be mixed with water for forming a desired lubricant emulsion. The lubricant is comprised of 20 to 60 wt % oil, 20 to 59 wt % solid aliphatic mono carboxylic acids with 10 to 30 carbon atoms, 1 to 15 wt % alkanol amine with 2 to 5 carbon atoms, to 15 wt % emulsifier, 0.05 to 2 wt % aromatic sulfonate, and 2 to 15 wt % monoalky or dialkyl phosphate with 8 to 20 carbon atoms in the alkyl group, and optionally 1 to 5 wt % liquid fatty acid with 12 to 22 carbon atoms in combination with 4 to 8 wt % aliphatic fatty acid amide with 10 to 18 carbon atoms. For producing the emulsion with water, a temperature of more than 60° C., preferably between 80 to 90° C., is required.
Due to the reduced corrosion protection, aqueous lubricant emulsions are however not suitable likewise as pre-lube for steel and aluminum.
A dry pre-lube lubricant (hot melt) that is said to be washed off “cold” is disclosed in U.S. Pat. No. 5,069,806. This lubricant, applied in melted form on the steel strip so that a flexible solid lubricant film is obtained after cooling, can be washed off by an alkaline solution at a temperature of 49 to 60° C. (120 to 140° F.). It is based on 80 to 90 wt % of a substantially saturated refined ester which is formed of an aliphatic, polyhydric alcohol and a C2-C6 carboxylic acid. Preferably, this is a hydrogenated tallow triglyceride lubricant base. Further components are 4 to 14 wt % partially esterified plant oil (castor oil) as a softener and 2 to 6 wt % surfactant that can be an aromatic polyether (reaction product of an aromatic C14-C20 alcohol with 5 to 15 mol ethylene oxide and 10 to 20 mol propylene oxide per mol alcohol), stearamide alkanol amide, iso-stearamide alkanol amide, a mixture of an aspartic acid diester and oleic acid, imidazolins or mixtures thereof. As a film reinforcer, 0.1 to 2 wt % of an ethylene-carboxylic acid-copolymer is employed; optionally, the lubricant can also contain additionally as a corrosion inhibitor 0.1 to 3 wt % of an antioxidant, preferably of the hindered phenolic type.
Based on this prior art, it is object of the present invention to provide an improved lubricant composition that can be washed off cold for application on a metal strip that can be used as pre-lube or corrosion protection, forming and/or washing oil. Washing off cold is to be understood here as removal of the lubricant with an aqueous alkaline cleaner, for example, in a cleaning bath, at room temperature or without additional heating of the cleaning bath, i.e., significantly below the usual temperatures of 49 to 60° C. in the prior art.
At the same time, the lubricant composition should exhibit protection from corrosion and from adhesion of the metal strips, satisfactory lubrication action for forming processes as well as compatibility with all downstream manufacturing steps. Moreover, the lubricant composition should form a stable and homogenous film after application on the metal strips, be inexpensive in manufacture and disposal, be simple in regard to handling, and suitable for various steel and aluminum qualities.